NEWARK, N.J. — A federal jury Friday acquitted 20 reputed mob figures of racketeering charges, ending what is believed to be the nation's longest federal criminal trial and handing the government a stunning defeat.

The jury, which had been selected 21 months ago, read 77 separate innocent verdicts before the courtroom erupted in pandemonium. The defendants and their attorneys hugged and gave a standing ovation to the jury, which had deliberated just 14 hours. The jury forewoman wept.

"What's there to say?" Assistant U.S. Atty. V. Grady O'Malley said. "Apparently the jury just resented the length (of the trial) and the breadth of the indictment."

'We Own New Jersey'

The government had charged that Anthony (Tumac) Accetturo of Hollywood, Fla., and his co-defendants controlled a powerful New Jersey faction of the Lucchese organized crime family that had illegal gambling, loan-sharking, drug-dealing and fraudulent credit-card operations.

Prosecutors had described the 20 defendants as virtually the entire New Jersey membership of the Lucchese family and contended that they boasted, "We own New Jersey."

The defense tried to discredit government witnesses, many of whom had serious criminal records. The government contended that only such insiders could tell the story of the organized crime family.

Defense attorney David Ruhnke said the verdict was a "complete rejection" of long government racketeering prosecutions against numerous defendants.

Defense lawyers described the prosecution as "gratuitous" and said they were not surprised at the quick verdict, which they said bore out their argument that the government had no case.

More than six weeks of closing arguments began on July 8, after the defense rested without producing a single witness. Defense lawyers said there was no need for the defendants to testify because the prosecution's case had broken down on cross-examination.

Client 'Thrilled'

"We think this is certainly the last prosecution that can be brought like this," added defense attorney Miles Feinstein.

"My client is enormously thrilled by the result," said Accetturo's attorney, Stephen Skoller.

"I'm just glad it was everybody (acquitted)," said Michael Taccetta, a Florham Park resident charged with supervising the organization in New Jersey.

The defendants and their lawyers waited outside the courthouse to applaud the jurors as they emerged before going to a restaurant to celebrate. Some of the jurors blew kisses, waved and smiled broadly. All declined comment, driving off in a government van.

Before they were dismissed, U.S. District Judge Harold A. Ackerman thanked the jury, saying, "I commend you in the highest terms for your dedication, your patience, your attentiveness."

"I'm just glad it's over," the judge said later, adding that he planned to go on vacation as soon as possible.

89 Witnesses

The panel began deliberating Thursday morning with a record to consider that included 40,000 pages of transcripts, testimony from 89 witnesses and 850 exhibits, including 400 tapes.

The government's star witness was Joseph Alonzo, a diagnosed schizophrenic, admitted drug addict and alcoholic and convicted criminal who had shot one of the defendants--his cousin--five times.

Defense attorney Robert L. Brown, elected mayor of Orange during the trial, criticized the government for calling "liars, thieves, crooks and criminals" as witnesses.

Michael Critchley, who represented Taccetta, called the verdict a "collective victory."

"The odds in this one were against 1,000 to 1," he said.

Critchley had said the jury's interest in the opening arguments was a good sign for the defense.

"We had contended all along the government promised much more (in its opening) than they were able to deliver," he said. "The government said they would bring loan-shark victims in (to testify) and they didn't. They promised testimony of people they never produced."

Pictures of Gangsters

The government had alleged that the defendants, charged in an indictment unsealed in March, 1986, operated out of the Hole-in-the-Wall luncheonette in Newark, where pictures of gangsters Al Capone and Meyer Lansky hang on the wall. Witnesses testified about kisses of respect for the boss, "tribute" payments and mob "sit-downs."

U.S. Atty. Samuel A. Alito Jr., who came to office after the indictment was unsealed in August, 1985, said he had no regrets about the prosecution but in the future would try to keep cases "as short and simple as possible."

"Despite this loss, the days of the Mafia are numbered," Alito said.

According to the Administrative Office of the Courts in Washington, the trial surpassed in length the "Pizza Connection" heroin-smuggling case, which ended after 17 months in March, 1987.